1. Technical Field
The present invention relates to a heat sink, a semiconductor device, and a method of manufacturing a heat sink, and in particular to a heat sink which has a combined structure composed of a recess and a projection, a semiconductor device having the thus-configured heat sink, and a method of manufacturing the thus-configured heat sink.
2. Background Art
Advanced semiconductor devices have recently been becoming more heat emissive, with the progress of improvement in the operation speed. The semiconductor device may therefore be provided with a heat sink on one surface thereof, aiming at ensuring efficient heat radiation. FIG. 12 is a drawing illustrating a general configuration of a conventional semiconductor device 50.
The semiconductor device 50 contains an interconnect board 1, a semiconductor chip 2 mounted on the interconnect board 1, and a heat sink 9 disposed over the semiconductor chip 2. Illustrated herein is an exemplary case where the semiconductor chip 2 is bonded to the interconnect board 1 while placing bumps 3 in between, by flip-chip bonding. The semiconductor chip 2 is electrically connected through the bumps 3 to terminals on the interconnect board 1, and adhered to the interconnect board 1 while placing a resin layer (underfill) 6 in between. On the outer periphery of the semiconductor chip 2 on the interconnect board 1, a reinforcing plate 5 is provided. The reinforcing plate 5 is adhered to the interconnect board 1 while placing an adhesive layer 4 in between. The heat sink 9 is adhered to the semiconductor chip 2 and to the reinforcing plate 5, while placing a resin layer 7 and an adhesive layer 8, respectively, in between. The resin layer 7 may be configured by a material, such as an electro-conductive paste, having a large thermal conductivity. On the surface of the interconnect board 1, opposite to the surface having the semiconductor chip 2 mounted thereon, external terminals 10 are provided.
In the process of assembly of the semiconductor device 50 illustrated in FIG. 12, a problem has been known in a step of disposing the heat sink 9 onto the semiconductor chip 2 of each semiconductor device 50. The problem will be explained referring to FIGS. 13A and 13B. In the process of bonding the heat sink 9 using an automated machine, the heat sinks 9 before being bonded are housed in a predetermined space in the machine, and then fed out therefrom for bonding. Larger number of heat sinks 9 housed therein may be efficient, in view of reducing the number of times of supplementation. For the purpose of increasing the number of housing, the heat sinks 9 are often kept stacked in the vertical direction. One heat sink 9 is picked up by a suction head 11 from the stack of the heat sinks 9, as illustrated in FIG. 13A, and is then transferred. However, in this process, a plurality of heat sinks 9 may occasionally be picked up under suction, and may be transferred in a stacked manner as illustrated in FIG. 13B.
Japanese Laid-Open Utility Publication No. H06-38257 describes a configuration of a heat sink having, on one surface thereof, a projection-like plated film formed at each of four corners. This configuration is reportedly successful in preventing the heat sinks from being picked up under suction in a stacked manner. According to the configuration described in the publication, the projections are provided on one surface of the heat sink by plating. According to the description, the heat sink herein is typically composed of copper, iron-nickel alloy or the like, and the plated film may therefore be formed by spot plating directly onto the heat sink.